Railroad hopper cars are used to transport bulk lading through railway systems. A railroad hopper car typically includes discharge gates located on the underside of the car for unloading the transported materials. Discharge gates typically include one or more sliding panels that may be selectively moved between open and closed positions to expose or cover an opening in the undercarriage of the car. Typically, an opening and closing drive mechanism shifts a panel between open and closed positions via a rack or racks fixed to the panel and an operating shaft. The operating shaft carries pinions which engage the racks. The operating shaft is rotated to move the panel in the desired direction. The car may be unloaded by sliding the panel to open the gate and allowing the lading to flow through the opening.
Often the materials transported comprise granular or particulate matter such as sugar, flour, grain, plastic pellets and cement. Conventional methods used to unload hopper cars include gravity discharge, vacuum discharge and pneumatic sled discharge, depending on the nature of the material transported.
During gravity discharge, lading falls from the car through a discharge opening in the gate by gravity. During vacuum discharge, lading falls from the car and through an opening in the gate into a closed vacuum chamber. Vacuum nozzles, in communication with the vacuum chamber, may project from the outer surface of the gate. A vacuum hose is connected to one or more of the vacuum nozzles and vacuum is applied to the hose. Air drawn from the car and through the gate carries lading into the vacuum chamber, through the vacuum nozzles and into the hose. During pneumatic sled discharge, a pneumatic sled is attached to the bottom of the discharge opening. The pneumatic sled includes screw type conveyors for discharging lading from the hopper car. Compressed air is blown into the discharge opening to pressurize the inside of the hopper car and separate compacted lading. The lading falls through the discharge opening and into the screw conveyors for removal.
In the case of high volume unloading, gravity discharge may be readily accomplished by simply opening the hopper car discharge gate and allowing the lading to flow downward through the gate. Gravity discharge is a common method of unloading used for materials such as unprocessed grains, feed, fertilizer, sand and soda ash. In the case of fine materials such as sugar, flour or cement, difficulties may be encountered during discharge due to significant quantities of the material becoming airborne. Such difficulties can lead to product contamination. In addition, fine materials may tend to accumulate on or within the elements of the discharge gate causing reduced outward flow of the lading, clogging of the discharge opening, and/or malfunction of the gate.
Unloaders may attach a boot to the bottom of a gravity discharge gate to feed lading to an enclosed screw conveyor. Attachment of a boot, however, is slow and awkward and the area of the gate where the boot attaches may not be sanitary. Therefore, many handlers of finished food products such as sugar and flour, and plastic pellet handlers, prefer vacuum unloading or discharge. Discharge of fine materials may accomplished using vacuum discharge methods which can increase material flow and reduce airborne particles in the work environment proximate to the gate. Vacuum discharge is particularly preferred where avoidance of contamination is important.
Difficulties in the prior art devices, however, persist relative to the seals formed between elements within the gate assembly, particularly between outer hopper or frame elements and sliding panels. Gaps between sealed components may be present as a result of dimensional variations in conventional multi-bend fabrication. In addition, surfaces for supporting the panels are prone to fouling due to build-up of transported matter, and wear due to friction caused by repetitive sliding of the panels over the support surfaces.